<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>let 命令-不允许重复声明</title>
<script>
var x = 3;
var x = 4;
 console.log(x); // 单独运行结果为 4
 //如果与下面代码一起运行，则无结果，因为下面代码属于编译错误

 let y = 1;
 let y = 2;
 console.log(y); // Identifier 'y' has already been declared 
 </script>
 </head>
 <body></body>
 </html>